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Re: [ANNOUNCE] Ramback: faster than a speeding bullet

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To: Alan Cox <alan@...>
Cc: <linux-kernel@...>
Date: Monday, March 10, 2008 - 11:50 pm

Hi Alan,

Nice to see so many redhatters taking an avid interest in storage :-)

On Monday 10 March 2008 02:22, Alan Cox wrote:

Right, and now with ramback you will be able to preserve that state and
have the performance too.  It is a wonderful world.


I was alluding to to e2fsck's amazing repair ability, not ext3's journal.


But that does not satisfy the requirement you snipped:

 * Applications need to be able to read and write ramback data during
   initial loading.


More accurately: in general, cannot transfer directly.  The ramdisk may
be external and not present a memory interface.  Even an external
ramdisk with a memory interface (the Violin box has this) would require
extra programming to maintain cache consistency.  Then there is the
issue of ramdisks on the way that exceed the 40 bit physical addressing
of current generation processors.

Even for the simple case where the ramdisk is just part of the kernel
unified cache, I would rather not go delving into that code when these
transfers are on the slow path anyway.  Application IO does its normal
single copy_to/from_user thing.  If somebody wants to fiddle with vm,
the place to attack is right there.  The copy_to/from_user can be
eliminated (provided alignment requirements are met) using stupid page
table tricks.  In spite of Linus claiming there is no performance win 
to be had, I would like to see that put to the test.


Sorry, I failed to parse that.


"640K should be enough for anyone"

http://www.violin-memory.com/products/violin1010.html <- 504 GB ramdisk


The finer the granularity the faster the ramdisk syncs to backing
store.  The only attraction of coarse granularity I know of is
shrinking the bitmap, which is currently not so big that it presents
a problem.

Your comment re fs chunk size reveals that I have failed to
communicate the most basic principle of the ramback design: the
backing store is not expected to represent a consistent filesystem
state during normal operation.  Only the ramdisk needs to maintain a
consistent state, which I have taken care to ensure.  You just need
to believe in your battery, Linux and the hardware it runs on.  Which
of these do you mistrust?

Regards,

Daniel
--
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Messages in current thread:
[ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Mon Mar 10, 2:46 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Wed Mar 12, 1:27 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 1:22 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Chris Snook, (Mon Mar 10, 2:49 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Artur Skawina, (Mon Mar 10, 10:51 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Mon Mar 10, 11:50 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Wed Mar 12, 1:29 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Thu Mar 13, 1:39 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 2:14 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 3:14 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Willy Tarreau, (Sat Mar 15, 4:59 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 5:25 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 5:51 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 5:17 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Sun Mar 16, 1:42 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Krzysztof Halasa, (Sun Mar 16, 6:15 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 16, 6:38 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Krzysztof Halasa, (Sun Mar 16, 7:08 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 16, 7:43 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 16, 4:48 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Bernd Eckenfels, (Sat Mar 15, 7:18 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Willy Tarreau, (Sat Mar 15, 5:54 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 6:33 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Willy Tarreau, (Sat Mar 15, 7:22 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 11:33 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Krzysztof Halasa, (Sun Mar 16, 6:02 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Theodore Tso, (Sun Mar 16, 3:04 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Willy Tarreau, (Sun Mar 16, 2:56 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Krzysztof Halasa, (Sun Mar 16, 6:12 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Sun Mar 16, 1:24 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Krzysztof Halasa, (Sat Mar 15, 7:57 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 6:00 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 16, 5:57 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Sun Mar 16, 9:31 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 16, 10:42 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Mon Mar 17, 1:52 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Mon Mar 17, 3:14 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Mon Mar 17, 4:25 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Pavel Machek, (Sun Mar 23, 5:33 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 23, 4:44 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Mon Mar 17, 2:56 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Mon Mar 17, 4:16 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Willy Tarreau, (Mon Mar 17, 1:30 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Ric Wheeler, (Mon Mar 17, 9:52 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 16, 6:36 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sun Mar 16, 7:39 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Rik van Riel, (Thu Mar 13, 4:27 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 10:23 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, John Stoffel, (Fri Mar 14, 10:00 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Fri Mar 14, 1:22 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Fri Mar 14, 1:42 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Chris Friesen, (Wed Mar 12, 2:11 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Wed Mar 12, 6:56 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Thu Mar 13, 1:45 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 2:17 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 3:12 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 5:49 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 4:06 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 5:16 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Pavel Machek, (Sat Mar 15, 4:18 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 4:51 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 3:32 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Thu Mar 13, 3:50 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 4:03 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Pavel Machek, (Sat Mar 15, 4:26 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 5:05 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Mike Snitzer, (Sat Mar 15, 4:40 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Thu Mar 13, 2:30 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 2:50 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Pavel Machek, (Sat Mar 15, 9:32 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 4:22 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Pavel Machek, (Sat Mar 15, 5:33 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Sat Mar 15, 5:47 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, David Newall, (Thu Mar 13, 3:05 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 3:13 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Artur Skawina, (Tue Mar 11, 9:32 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Artur Skawina, (Tue Mar 11, 10:31 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Rik van Riel, (Mon Mar 10, 3:01 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 12:28 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Grzegorz Kulewski, (Mon Mar 10, 3:51 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Mon Mar 10, 4:23 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Lars Marowsky-Bree, (Mon Mar 10, 5:03 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 7:14 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Lars Marowsky-Bree, (Tue Mar 11, 7:23 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 7:50 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Lars Marowsky-Bree, (Tue Mar 11, 5:56 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Ric Wheeler, (Thu Mar 13, 9:27 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 3:02 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Ric Wheeler, (Thu Mar 13, 3:12 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 3:38 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 7:30 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 7:02 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Matthias Schniedermeyer, (Thu Mar 13, 5:15 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Chris Friesen, (Tue Mar 11, 1:26 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 3:56 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Willy Tarreau, (Tue Mar 11, 4:53 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Wed Mar 12, 4:17 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Rik van Riel, (Thu Mar 13, 4:34 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Thu Mar 13, 10:20 pm)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Mike Snitzer, (Wed Mar 12, 10:41 am)
Re: [ANNOUNCE] Ramback: faster than a speeding bullet, Daniel Phillips, (Tue Mar 11, 12:23 am)
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